Text entry is one of the most frequent human/computer interaction tasks. Although speech and handwriting recognition techniques by computers have improved, typewriting (or keyboarding) remains the main text-entry method. Once learned, touch typing on a keyboard offers two critical characteristics: rapid speed and attention on the screen. A skilled typist can type over 60 words per minute, far beyond the typical 12 words per minute produced by handwriting. In addition, touch-typing frees the user's visual attention so the user can focus on the text entry task instead of the keyboard or hands.
Numerous difficulties in touch-typing arise when the text-input language is Chinese (or any other language based on logographic characters). Currently, one of the most popular methods used for Chinese text input is pinyin input. Pinyin, approved in 1958 by the Chinese Government, is the official Chinese phonetic alphabet based on Roman characters. For example, in pinyin the Chinese character  (center, middle) is “zhong” and the pinyin for the word “” consisting of two Chinese characters is “Beijing”. An overwhelming majority of computer users in China use pinyin or some variation of it for computer input. Other non pinyin-based Chinese text input methods exist for encoding the logographic Chinese characters, but the amount of learning and memorization required by these methods has prevented them from becoming popular.
The complication to pinyin input is that most Chinese characters are homophonic on a wide scale. In Mandarin Chinese, there are only about 410 distinct syllables while there are 6,763 Chinese characters in the national standard database GB2312. Consequently, each syllable corresponds to 16.8 characters on average, notwithstanding the relatively small number of characters with multiple pronunciations. When a user types the pinyin of a character such as “zhong”, the computer software for Chinese text input displays many candidate characters with the same pronunciation, numbered for selection purposes. The display is typically a “page”, usually a one-line graphical window. The first eight candidate characters for “zhong” could be 1  2  3  4  5  6  7  8  having the following meanings:
1. center; 2. type; 3. heavy; 4. mass; 5. kind; 6. finale; 7. loyal; and 8. swollen, respectively.
The user must then select a choice from the candidate list by typing the identifying number, e.g., the number “1” for the character corresponding to “center”. If more than eight characters correspond to a pinyin word, pressing the “page down” key displays additional candidates also numbered 1 to 8 which may be selected as before.
This multiple choice selection process renders current pinyin input much less efficient than typing in alpha-based languages. A major source of this inefficiency is the difficulty of touch-typing a numeric key to select the target character. On a standard “QWERTY” keyboard typing the numeric keys may be much more difficult than typing the alphabetic keys. This is due in part to the distance between the numeric keys and the “home row” where the hand naturally rests during typing, i.e., the ASDFGHJKL keys.
In addition, many if not most typists have to look at and then type the numeric keys. If the character candidates for the pinyin word exceed one “page”, the typist must also “page down” to view additional candidates, consuming additional time. Consequently, the two important advantages of touch-typing, speed and the low demand for visual attention, both suffer when Chinese input is required. A text entry system for Chinese input that avoids numeric keying and thus maintains the user's touch-typing ability is a compelling goal in Chinese text input.
Another source of inefficiency in Chinese language text entry is the choice reaction time, i.e., the time required to choose the correct character from the list presented by the text entry software program. Numerous methods have been proposed to reduce the frequency and number of choices in pinyin-based input.
These methods can be categorized in the one or more of the following five categories:
1. Using additional keystrokes to represent the shape or structure of a Chinese character.
2. Enabling the user to input both characters and words. A Chinese word is usually composed of one, two or three Chinese characters. If the user types the pinyin of “” (Beijing) separately as ‘bei’ and ‘jing’, the two syllables have 29 and 40 candidates respectively. If the user types them as one unit, then only two candidates “1  2 ” (1. Beijing; 2. Background) are likely choices in daily language.
3. Using a Chinese language model to reduce the uncertainty at the phrase or sentence level. The language model can either be rule-based or based on bigrams or trigrams, which are commonly used in speech recognition.
4. Adding the Chinese intonation information after the pinyin of a character (the four tones in Chinese pronunciation are often encoded as 1–4 for addition entry).
5. Continuous completion, wherein the system continuously composes possible choices based on the pinyin characters typed. As the pinyin stream grows longer, the number of possible choices is reduced until the user decides to select a character.
Though the foregoing proposed measures help to reduce the choice reaction time, they do not completely eliminate it. A system is therefore needed to further minimize the amount of time and attention required to choose and enter the appropriate character.
Current eye-tracking technology uses the eye gaze as a direct control channel to move a cursor on the screen, or to assist in entering text. Reference is made to U.S. Pat. No. 5,859,642 to Jones, and Zhai, S. Morimoto, C., Ihde, S., “Manual And Gaze Input Cascaded (MAGIC) Pointing,” Proc. CHI' 99, pages 246–253, Pittsburgh, Pa., USA, 15–20 May 1999. However, there are two deficiencies in using eye-tracking technology for direct control. First, eye gaze cannot be very precise given the one-degree size of the fovea and the subconscious jittery motions that the eyes constantly produce. Second, the eye is not naturally suited for deliberate control functions. At times, eye movement is voluntary while at other times the eye moves involuntarily in response to external events. Current eye-tracking systems cannot easily distinguish deliberate eye movement from accidental eye movement.
To use eye-tracking technology in text entry of Chinese characters, a system is needed which allows the eye to select the desired Chinese graphic without requiring long-term deliberate control of the eye movement. Such a system would use eye movement to highlight the Chinese character while the user presses a key to select that character for entry. Alternatively, the system would use the eye gaze information implicitly when the user presses on a common or readily accessible, confirmation key that can be touch-typed, the candidate character the user is looking at is selected. The need for such a system has heretofore remained unsatisfied.